Oil cooling device



I .QEL im Filed Septl` 5, 1942 2 sheets-sheet 2 y. "nveutor: GAL-ORGE HERBERT /L.

Gltorueg Patented Sept. 4, 1945 on.l COOLING DEVICE George Herbert Gill, Los Angeles, Calif., assignor to The Garrett Corporation, Aresearch Manufacturing Company division, Inglewood, Calif., l a corporation of California Application September 5, 1942, Serial No. 457,461

8 Claims.

This invention relates in general to oil cooling systems for internal combustion engines. The invention has one application in the field of oil coolers for aircraft engines.

Oil coolers of the type now generally employed for aircraft installation comprise a cellular type of heat exchanger having inlet and outlet openings which are respectively connected in series with the oil circulating system, a means for regulating the cooling action of the heat exchanger, and some form of control for the regulating means which acts to provide a flow` of oil from the cooler to the aircraft engine within a temperature and viscosity range satisfactory for enicient operation and lubrication of the engine.

This invention relates in particular to the control for the regulating means of the heat exchanger.

The heat exchanger is an oil container, often in the shape of a cylindrical drum, through which oil passes from an oil inlet to an oil outlet in heat exchange relation with metal tubes within the drum, through which atmospheric air is passed by the action of the aircraft propeller, supercharger, or compressor means, or in consequence of the motion of the aircraft through the atmosphere.

The heat exchanger may include a supplementary oil container in the form of an oil jacket or mui surrounding a core or cooler proper in which the air tubes are mounted, or in the form of a separate compartment, within the cooling chamber, or both, through which oil as it comes from the engine may be passed to warm the cooling element.

To maintain constant the temperature of the oil leaving the cooler, the rate of transfer of heat units from the oil to the refrigerant air must be regulated to compensate for changing conditions of the oil and air streams. This regulation is accomplished in one type of cooler by varying the-rate of ow of air through the core by use of movable shutters, flaps, or other air stream controlling means which may be adjusted in position with respect to the direction of the flow of air for varying the flow rate of air through the core tubes in combination. with an actuating means for giving the shutters the movement of adjustment.

According to one type of oil temperature control, the means for regulating the position of the air stream shutters is controlled by a thermostat responsive to the temperatureV of the oil leaving the cooler, the shutters being opened or closed in correspondence with oil temperatures above or below the temperature desired for best engine operation.

The problem of oil temperature control is complicated by the fact that under certain conditions congealingor waxing of the oil within the core on the external surfaces of the air tubes or other heat exchange Walls takes place due to an abnormally rapid transfer of heat from Vthe oil to the air or to an unduly prolonged period of transfer of heat from oil .to air at a moderately rapid rate. This condition usually arises from an excessively rapid drop in the temperature of the atmospheric air or a rapid increase of air now to which the thermostatic control cannot as rapidly respond. The formation of layers of waxed oil on the air tubes restricts the ow of oil through the core chamber, and may increase the pressure at the oil inlet of the cooler so as to build up a back pressure against the oil'circulating pump and cause diversion of a portion of the hot oil through the bypass passage.- Also, since the layers of waxed oil being o f low heat conductivity, act as heat insulators between theliquid oil and the air, the oil owing through the cooler in a restricted path at high speed leaves the cooler at an unduly high temperature. This hot oil is a disadvantage in the operation of the engine, and by causing the thermostat toy hold the shutters open, prevents the decrease lin the cooling action of the coolerwhich is necessary to melt the congealed oil. Excessive pressure may also develop in the cooler core in the Aabsence of waxing of oil on the air tubes if the core is lled with cold viscous oil when a cold engine is started, or for other reasons. -L

Itis an lobject of the invention to provide a cooling system in which the regulation of `the cooling medium, for example, air, is under control of the temperature of the oil which'has been cooled, modied by pressure changes which occur in the cooler, whereby anincrease in pressure in the cooler due to cooling or a tendency ofA the oil to congeal will result in a corresponding decrease in the effectiveness of the cooling medium to offset this tendency for the oil to congeal.

One object of the invention islthe: provision of a cooling system of the character described having a, thermostatic control ofthe heat exchanger regulating means, in which the, fluid pressure drop between the cooler inletI and `cooler outlet is utilized under control of athermostat to oper? ate in either direction a reversible fluid pressure motor to open or close the shutters or other air ow regulating means in a simple,y eiective, and reliable manner. l

It is an object of the invention to provide a fluid cooling system with combined temperature and pressure control of the kind above described in which the temperature and pressure controls are combined in a novel and eiective manner, aiording structural simplicity and reliability in performance. .A

It is an.objectiof'theinvention to provide a fluid cooling system having a combined temperature and pressure control in which a thermostat for effecting the temperature control is bodily movable by fluid pressure operative device-responsive to the pressure dropin-4 the cooler in a manner to modulate the control/action of the thermostat on the shutter operating means.

It is another object of the invention to provide a fluid cooling system having a combined temperature and pressure'control in which'the temperature control is modulated by a uid pressure operated means responsive to pressure drop in the cooler. y

It is a further object of the inventionfto provide .afdevice ofthe character described in which a 4thermostat-isibodilyzmovable by reason of its connectionto za' movable wa1l,.the two active faces of whichiare exposed to fluid pressure communicatedvto themovable wall from two relatively spaced stations alongthe flow path of the fluid stream.

It.is.stillranother-object-of the invention to providela'fluidcooling system having a combined temperature and pressure control in which a thermostat for effecting the temperature control is inthe form of a spiraland isr bodily rotatable by a fluid. pressure device responsive to the pressure drop inthe cooler and particularly by a hydraulic motorsuitablyconnected tothe-inlet and outlet passages ofthe cooler.

It isalso an object of the invention to provide aiiuid cooling'system having a combined'temperature and pressure control in which a spirally formedfthermostat `for accomplishing the temperature` control isbodily operated by a hydraulic motor connected to-I the inlet vand outlety passages ofthe cooler bymeans of an overrunningscrew and nut connection between a non-rotatable piston ofithe'hydrauliomotor andl the dead end of the thermostat.

.'.Itislanother object of the invention to provide afluid cooling system havinga combined temperature and pressure control of the kind above described inwhich a normally closed valved''bypass .passage is provided for the relief of the `cooler chamber from excessive pressures in the inlet piping, in which the cooler chamber isprotected from' excessive backpressures inthe outlet piping and in which-the thermostat for accomplishing temperature'control under the modulating influence of the pressure drop between the inlet and outlet passages is disposed downstream'from the bypasspassage and from the devices for protecting Vthe cooler'chamber from back pressures in the outlet piping.

Further' objects and advantages of the-invention will be brought out in the following part of thev specification.

Referring tothe drawings, which are for illustrative. purposes only,

Fig.) 1 is :a vertical sectional view showing a controltting and adjacent portions ofl a cooler embodyingl the invention.

Fig. '12 isa'horizontal sectionalview taken as indicated bylines`2-2 of Fig. 1.

Fig. 3'is a sectional view taken as indicatedvby the lines 3-3 of Fie. 2. v

zdrum II.

Fig. 4 is a schematic view indicating the airv Van-inlet-chamber I5, a muff outlet chamber I6,

and a core outlet chamber I'I. The inlet chamber I5 has an inlet opening I8 and its lower open side registers with an inlet opening I9 in the The inlet chamber I5 is also formed with an opening I9 communicating with one end of the muil chamber.

The muff outlet chamber I6 which communicates with the outlet end of the mui through an opening (not shown) is formed with an outlet openingfZI `in the upper wall of the fitting I4. -The ycore outlet chamberllhas its lower open side in registry witha core outlet opening 22 in the drum II and is formed with an outlet opening23. f

' `A controltting 24 is secured`to the fitting I4. It is formed with an inlet chamber 25 which receives oil from the hotoil delivery piping of the engine 'through 'a port lopening Z6. It is also formed with an outlet chamber-21 from which oil is Withdrawn into the cooled o il return piping tothe engine through an outlet port 28;

The outlet chamber 2 has'a core inlet opening 29 registering with the opening 23 ofthe core outlet chamber I1 of theiitting -I4 and has an opening 28a registering vviththe mun outlet opening 2| of the chamber ls of the-fittingiu. The-walls of the tting 24 are alsoformed with lan opening Silbetween' the inlet chamber 25 and outlet chamber 21. The openings 28a, 29, and 30 are fitted with valve seats 3|, 35, and 39 respectively Y -A poppet valve structure 32 having a valve closure-'33 engaging the-valve seat 3 Iand a spring 34under pressure conditions attendant upon the normal operation of the cooling system-prevents iiow of oil through the opening 28a from the muff outlet to the outlet chamber 21 and 'also protects the muil chamber from back pressures of excessive value in lthe cooled o'il lreturn piping. The spring f34 is gauged to permit lifting-of the valve closure'33 whenpressure in the mu' outlet chamber IB-vand pressure in the inlet chamber I5-which serves both the core chamber and themui chamber becomes sufliciently high to endanger the walls of other structural elements of the cere and muff.

A similar poppet valve structure 3Q has a valve closure '31 which engagesthe valve seat-35. `The spring `38 of'thisfvalve structure 38 is -gauged to holdthe valve closure`31'open in response to light pressures within the core chamberY `such as are attendant upon its normal operation, but will cause .a seating of the valve closure V3'! in response to even alight back pressure in theoutlet chamber 2l arising from a back pressure surge inthe return piping to the engine.

Oilreceived from the engine into the chamber 25 may pass from that chamber into the inlet chamber I5 or the outlet chamber 21 as determined' by' the operation of a valve structure 40. -A cup shapedlpistonfllI has a' pistonl head'42 exposed on its lower face to the pressureof oil in the chamber "2 5- and`has a'cylindrical piston wall 43extending upwardly from the piston head 42 and having cooperative sliding engagementwith the inner face of a cylinder 44 mounted by means of a threaded plug 45 integrally formed with the cylinder in the upper wall of the tting 24. The plug 45 has a port 46 which subjects'the space or chamber 41 within the cylinder to the atmospheric pressure exterior to the fitting 24. Since, then, the upper face of the piston head 42 is subjected to atmospheric pressure, any super atmospheric excess in fluid pressure `within the chamber 25 will be eiective to move upward the piston 4|. This movement is opposed by a spring 48 seated betweenthe plug 45 and pistonV head 42. As shown in the drawings, this spring takes the form of a double coiled spring seated under compression in the chamber 41.

The piston 4| is formed with a valve face 49 Awhich cooperates with the valve seat 39 to control .iiow of oil from the inlet chamber 25 to the outlet chamber 21 through the annular opening formed between the Alower end of the cylinder 44 and the valve seat 39. Guide tongues D depending from the piston head 42 slidably engage the bore of the valve seat 39 to keep the piston axe iallyaligned with the valve seat. v,

A valve stem 5| is secured at its upper end to the piston head 42 and extends downwardly through the valve chamber 25 and mounts on its lower enda valve closure 52 having a valve face 53 disposed to cooperate with the valve seat 55 andV so spaced from the valve face 49 that, when the latter is in seated position, valve face 53 is displaced downwardly from its valve seat 55 al,- lowing oil to flow from the inlet chamber 25 through the port 54 into'the inlet chamber |5. When, on the other hand, the valve face 53 is seated against the valve seat 55, the valve face 49 is displaced above its valve seat 39, allowing oil to flow from the inlet chamber 25 into the outlet chamber 21. i

Under normal pressure conditions within the inlet chamber 25 the spring 48 holds the valve 49 in closed position and the valve 52 in open position, allowing oil from the engine to ow through the inlet chamber 25 into the heat exchanger inlet chamber I5 from which it may p-ass either through the core chamber or the mui chamber, as will be later explained. When, however, pressure in the inlet chamber 25 rises to an excessive value, the piston 4| is moved upwardly, lessening the iiow of fluid by valve 52 and opening the valve 49, permitting a portion of the oil stream in the inlet chamber 25 to flow directly into the outlet chamber 21 and thence to the return piping to the engine, protecting the heat exchanger chambers from such excessive pressure in the inlet chamber 25. When the inlet pressure reaches a prescribed value, the valve 52 V will close against its seat and the valve 49 will be elevated to its completely open position. The

valve structure may move with a quick snap action from its lowermost to its uppermost position in response to a suddenly occurring pressure surge. These excessive pressures are usually caused by a rapid rise in pressure in the inlet piping generated by the scavenging pump at the engine, but the development of an excessive pressure may be facilitated when the mui and core chambers of the heat exchanger are filled with cold oil when the engine is started or by excessive congelation of oil within the core chamber. Under any condition which may cause upward movement of the valve stem 5|, both elements of the heat exchanger are ,bypassed until pressure in the chamber 25 recedes to a norma-lvalue.'

-v Upward movement of the valve structure 40 is initiated by the difference between the pressure in the chamber 25 on the area of thevalve seat opening3l9y and the force exerted by the ,spring 48. AOn the other hand, after the valve structure 4|] has reached its extreme upper position and the .valve face 53 has engaged the valve seat 55, the valve structure 49 is held in itsuppermost position against the action of the spring 48, not only bythe heat exchanger back pressure on the under face of the valve52, but also by the pressure in -the chambers 25 and 21 exerted over an area whichis the diierence in the area of the valve seat opening 39 an-d the cross-sectional area of the cylindrical chamber 41. This follows because the total pressure acting on the valve 52 within .the valve seat opening 55 is balanced by the vtotal pressure acting on that part of the valve face 49 within the valve seat opening 39, these openings having the same diameter. The above dened areal difference is the area of the horizontal projection of the annulus of the valve face 49v outside of the valve seat 39. The pressure on this annular area acts as a safetyfactor vto hold valve 52 in closed position and prevent a chattering movement thereof Vuntil the pressure in the vchamber 25 has dropped below the danger point and the pressure in vthe chamber I5 is a substantial degree less than that in the chamber 25. This performance characteristic of the valve structure 49 gives additional protection tothe two'chambers of the heat exchanger.

f Flow of oil from the inlet piping, leading from the engine, to thereturn piping to the engine mayqfollow any one of three paths through the tting 24 and heat exchanger as determined byithe positions ofthe several valve devices 49, 32,` and 36.

Under normal conditions oil enters through the inlet port 2B into the inlet chamber 25 as indicated by arrows F in Fig. 2. Thence it passes into 'theheat exchanger inlet chamber I5 as indicated by arrows A in Fig. l, from which chamber it passes through the core [chamber as ine dicated by arrows B, and after passing through the core chamber in contact with the air tubes |2, passes through the core outlet chamber |1 into the outlet chamber 21"'as indicated also by arrows B. From the outlet chamber 21 it leaves the fitting through the port 28 passing into the return piping to the engine as indicated by the arrows C.

If a heavy. back pressure develops in the core' chamber, the valve 33 is lifted, permitting oil to pass from the inlet chamber 25 intothe heat exchanger inlet chamber I5, as indicated by arrows A,.and thence, as indicated by arrows D, through the muli chamber to the mui outlet chamber I6, opening 28a, andthe outlet chamber 21, from which it passes vinto the return piping leading tothe engineas indicated by arrows` C in Fig. 2.

If thepressure in the chamber 25 rises toan excessive value the valve structure 40 is lifted and oil passesfrom the inlet chamber 25 through the port opening 3D directly into the outlet chamber 21, as indicated by arrows E, from which it enters thereturn piping tothe engine, as indicated by arrows C.

High pressure in the outlet chamber 21 generated, for example, by some conditions in Ithe return piping to the engine causes an i-mmediate seating of the check valve structures 36 and 32,

and* moves the valve structure 40, if .alreadyl partly open, to its uppermost position, closing the outlet ends oftheport chamber and muff respectively, as well 4as the commonfinletendiof these chambers `at the .port opening 54. If at the moment of a high pressure surgein the return pipinggthevalve face`53 is in seated position and remains seated, it .protects both the muff and core from the surge pressure at their inlet ends.

The means for regulating .the refrigerant may take any of the vforms-known to .the art. .The invention teaches ihow the regulating means, whether it is directly connected .,to the control thermostat or is operated by a motor under control of the thermostat, may be caused to actnot only in response to changes in the temperature in the oil, but in vaccordance with temperature changes modified by pressure conditions in the cooler. Thevmovable contact/arm 63, shown in Figs. 2 and 3, isbroadly presented as a control part yoperated in accordance with vtemperature changes modirliedby pressure .conditions in the cooler. By Iwayof example, it is shown as a contactor forming apart of an electrical shutter operating means, moreschematically presented in'Fig. y4, ofthe type disclosed inthe `copending application of Andrew L. Hannon, Serial No. 430,949, filediFebruary 14,1942, for Control devicefor oil `coolers'which has'issued as United StatesrPatent No. 2,314,937.

The passage of air through the tubes I2 is controlled lby the shutter means which yis schematically shownvinFig. 4. This shutter means is exemplified by the shutters 60 rwhich are adjusted between open and closedpositions by a linkagel. This linkis 'movedin either: direction'by a reversible electricmotor-BZ which is operated to place .the 'shutters 60 in any one of a. number of angularpositions through electrical circuits established by a movable contact arm 63asit engages theistationary contact/'64 vby means of a suitable conductor 65 connecting the stationary contact "64'withi a junctionA box 66 and the conductorssl connecting the junction box 66 with the motor62. Figs. 2 and 3 present a structural showing of the movable contact arm 6'3 andy stationary .contacts 564. contacts 64 are mountedv in an enclosed chamber 68 formed between a cover plate'and aportion of the wall of the fitting 24.

The movable contact arm-'63 is carried'lby a shasft110 suitably mounted Yin the wall `ofthe tting .24 and extending through Vthe fitting wall part way into the outlet chamber 21 where it is connected -to the live'end of a coil `or helical thermostat 1l. The :dead endof this thermostatis secured to a nuft'12 rotatablylmounted in a'partition wall 13 of the VFitting 24. The nut 12 Vthreadedly engages thepi'ston rod '13, the engaging threads having-an overrunning pitch to provide'forrotation of thenut .12 upon longitudinal movement of the rod 13.

The rod 13 is carriedf-byra piston `14 which slides within a cylindrical .chamber 15 :formed in the fitting 24 and closedat its outer'fendfloy a threaded plug 16.

The outer'end of the cylindrical chamber 15 is-connected to the inlet chamber 25by a duct passageway 11 and the inner end of the cylindrical chamber 15 is connecte'dto the outlet chamber 21 by a duct or passageway 18.

A key 80 engaging a key-way in the piston 14 preventsv rotative movement of the piston v14 within the cylindrical chamber 15. A springl urges the piston 14 rightwardtolward-retrazcted position in engagement with stops82 asshown inrFig.2.

The stationary fUnderznormal pressure conditions, thepiston 14 .is heldin this extreme4 right handpositlonby the spring-8L The nut `12 is also in its normal position holding'. the dead'end of the thermostat 1| stationary. Oilpassing through the heat exchanger expands and i contracts' the thermostat 1| aas its temperature increases or decreases, causing a rotative movement of the shaft 10 and the Acon-tact'arm B3 over thestationary contact 84 toregulate the position vof the lshutters .ini a mannerto return the temperature of the oil toits normal value. -When pressure withinthe core chamber Arisesvto an abnormal value dueto presence ofcold sluggish oil in the core chamber, asoccurs vwhenthere is danger of oil-congealing on the tubes l2, or when some congealing of oil has started, the pressure drop between inlet chamber 25.and the outlet chamber 21, applied tothefpistoni14 by-reason ofthe iiuid connections of the two ends of the cylindrical chamber 15 twith `the inlet chamber 25 and the outlet chambein21 through the passageways v11 and, moves the piston-in a leftward direction, causing rotation of A-the'nut 12 to an angle'corresponding to the longitudinalimovement of the piston 14 and piston rod 13.

The effect of the rotation ofthe nut'12 is to `cause ral'bodily rotation of the thermostat y1|, .and ia corresponding movement-of the control arm 4liti soas to closevthe shuttersisn beyond the position whioh'they would assume under .control ofzthe'thermostatalone thereby modifying the control lexercised by the thermostat; in a manner 'to reducethe airiow'below the value determined 'by the oil temperature applied to the thermostat. In consequence, the shutters 60, when there exists an abnormal pressure drop between thenlet and outlet ends of the cooler, are held in 'a relatively more closed position than under normal pressure conditions in response toany given temperature, reducing the rate of heat transfer vfrom oilrto air and permitting the cooler'to warm up.' If there is a severe congealing of oil on'the surfaces of the tubes l2, the piston will be moved tothe extreme leftward end of its'allcwable travel and the rotation of the thermostat will be of such magnitude that the control associated therewith will substantially completely close'the shutters 66.

AI claim as my-invention:

l. In an oil cooling system for an internal combustion engine, the combination of: an oil 'coolerhaving an oil inlet and an oil outlet; means associated with the cooler for varying the rate of flow' of a cooling fluid therethrough; delivery piping connecting the oil outlet of the engine with the oil inlet of the cooler; return piping connected to said cooler outlet to carry offthe cooled oil; a coiled thermostat responsive t0 the temperatureof the oil of the cooler and khaving a live end rotatable with respect to a normally fixed dead end with changing temperatures; means'actuated by movement of the live end of said thermostat for controlling said flow varying means; and means responsive tothe pressure drop between said oil inlet and said oil outletfor rotating said thermostat so as to change thel position of said live end thereof, said last-means comprising a hydraulic cylinder and piston device, the cylinder being connected at its ends to'saidinlet and outlet respectively, the piston 'being held `against rotation, and the piston being'connccte'dto rotate the dead end of. said .thermostat byan: overrunning screw and nut means.

2. In an oil cooling system for an internal combustion engine, the combination of: a cooler through which the oil is adapted to be circulated in heat exchange relation to a cooling fluid; means for varying the rate of flow of said cooling fluid through the cooler; a coiled thermostat; means normally holding one end of said thermostat against rotation; and means actuated by rotation of the other end of said thermostat in response to changes in temperature of the oil at a selected point in the system, for controlling said flow varying means, said holding means including a hydraulic cylinder, a piston axially slidable and non-rotatable therein, and an overrunning screw and nut interposed between said piston and said one end of Ysaid thermostat, said piston being adapted, in

response to a predetermined pressure drop across said cooler, to actuate said overrunning screw and nut so as to rotate said thermostat and thereby override the thermo-responsive action thereof and actuate said flow varying means to decrease the cooling capacity of the cooler.

3. In an o-il cooling system for an internal combustion engine, the combination of an oil cooler through which the oil may be circulated in heat exchange relation to a cooling fluid passing therethrough; -means for varying the rate of flow of said cooling fluid through the cooler; a coiled thermostat responsive to the temperature of the oil at a selected point in the system; means for normally holding a dead end of said thermostat in a xed position; and means actuated by rotation of the live end of said thermostat in response to changing oil temperatures for controlling said flow varying means, said holding means including means linearly shiftable under a predetermined pressure drop across said cooler and a screw jack interposed between said last means and said dead end of the thermostat, for rotating the thermostat, overriding the temperature responsive action thereof, and operating said flow varying means so as to reduce the cooling capacity of the cooler.

4. In an oil cooling system for an internal combustion engine, the combination of: a cooler through which the oil is adapted to be circulated in heat exchange relation to a' cooling fluid passed therethrough; means for varying the rate of flow of said cooling uid through the cooler; a coiled thermostat having a live end and a normally dead end and responsive to the oil temperature at a selected point in the system; means actuated by rotation of the live end of said thermostat in response to changing temperatures for controlling said flow varying means; and means for normally holding the dead end of said thermostat in a fixed position, said holding means including means responsive to a predetermined pressure drop across the cooler for rotating said thermostat so as to override the temperature responsive action thereof and operate said ow varying means so as to decrease the cooling capacity of the cooler.

5. In an oil cooling system for an internal combustion engine, the combination of: an oil cooler through which the oil may be circulated in heat exchange relation with a cooling uid passed therethrough; means for varying the rate of flow of said cooling uid through the cooler; a coiled thermostat responsive to the oil temperature at a selected point in the system; means including an electric motor and a switch having a pivotal arm rotated by the live end of said thermostat in response to changing oil temperatures for controlling the operation of said iiow varying means; and means for normally holding the other end of said thermostat in a fixed position, said holding means including means responsive to a predetermined pressure drop across the cooler for rotating said thermostat so as to override the temperature responsive action thereof and operate said iiow varying means to decrease the cooling capacity of the cooler to a minimum.

6. In an oil cooling system for an internal combustion engine, the combination of an oil cooler through which the oil may be circulated in heat exchange relation to a cooling fluid passed therethrough; means for controlling the rate of flow of said cooling fluid through the cooler; a thermostat responsive to the oil temperature at a selected point in the system; means including an electric motor and a multiple position switch including a switch arm actuated by the live end of said thermostat for controlling the operation of said iiow varying means; and means for normally holding the dead end of said thermostat in a fixed position, said holding means including means responsive to a predetermined pressure drop across the cooler for moving said thermostat so as to shift said switch arm to a terminal position in which it effects the operation of said flow varying means so as to reduce the cooling capacity of said cooler to a minimum.

7. In an oil cooling system for an internal combustion engine, the combination of: a cooler through which the oil may be circulated in heat exchange relation with a cooling fluid passed therethrough; means for varying the rate of flow of said cooling fluid through the cooler; a thermostat responsive to oil temperature at a selected point in the system; means including an electric motor and an electric switch, one contact of which is actuated by the live end of said thermostat for controlling the operation of said flow varying means; and means for normally holding the dead end of said thermostat in a fixed position, said last means including means responsive to a predetermined lpressure drop across the cooler for moving the thermostat so as to operate the switch in a manner to reduce the cooling capacity of the cooler.

8.' In an oil cooling system for an internal combustion engine, the combination of: an oil cooler through which the oil may be circulated in heat exchange relation to a cooling fluid passed therethrough; means for varying the rate of flow of said cooling fluid through the cooler; a thermostat responsive to oil temperature at a selected point in the system; means controlled by movement of the live end of said thermostat for operating said flow varying means; and means for normally holding the other end of said thermostat in a xed position, said last means including means responsive to a, pressure drop across the cooler in a predetermined amount for moving said other end of the thermostat and thereby moving the thermostat so as to override the thermo-responsive action thereof and operate said ow varying means so as to reduce the cooling capacity of the cooler. l

GEORGE HERBERT GILL. 

